1) Field of the Invention
The present invention relates to a seesaw balance type microminiature electromagnetic relay to be mounted on an exchanger or the like in a high density assembly and a method of producing the same. More specifically, it relates to a process of forming an armature unit in an integral form of movable contact springs having contact points and an armature operated by the attraction force of a magnet, and the structure of the armature unit.
2) Description of the Related Art
The seesaw balance type electromagnetic relay requires reduced installation and floor space thereby providing an advantage in that the available increase in the amount of circuits per printed circuit plate can facilitate an increase in the number of subscribers.
In such a microminiature type of electromagnetic relay, because very fine-structure parts must be assembled during the production process, a simplification of said structures is now in demand, thereby preventing complex production processes.
FIG. 1 shows an enlarged perspective view of a conventional monostable seesaw balance type microminiature electromagnetic relay. In FIG. 1, the electromagnetic relay 1 is comprised of, in broad classification, a casing 5, an armature unit 8, a substrate unit 9, and an electromagnet unit 10. The armature unit 8 is mounted onto common terminal pins 12 provided on the substrate unit 9, and the electromagnet unit 10 is provided between the armature unit 8 and the substrate unit 9.
The armature unit 8 is comprised of two movable contact springs 2 having protrusions 2a formed at the center thereof and contacts 2b formed at both respective ends thereof, an armature 6 having a non-magnetizing plate 3 on one end of the bottom face thereof, and a insert-molded insulator 7 having notches 7b for exposing the protrusions 2a of the movable contact springs 2. Since it is not shown in FIG. 1, the insulator 7 has a recess on a bottom face for exposing the protrusions (not shown) of the armature 6.
The substrate unit 9 is provided therein with a plurality of terminal pins 11 to 13 for connecting the unit externally. Terminal pins 11 and 13 each have a fixed contact 11a and 13a, and common terminal pins 12 have arc-shape grooves 12a and protrusions 12b formed at respective both sides of the arc-shape grooves 12a.
The electromagnet unit 10 is comprised of a U-shape yoke 14, an exciter coil 15 wound on the yoke 14, and a flat shape permanent magnet 16 that is fixed to join both ends of the yoke 14.
Because the protrusions 2a of the movable contact springs 2 engage with the arc-shape grooves 12a, the armature unit 8 can be pivotally disposed to the substrate unit 9. The protrusion of the armature 6 contacts a surface of the permanent magnet 16 set so that the non-magnetizing plate 3 confronts one-side end of the yoke 14.
The protrusions 12b are formed at both respective sides of the arc-shape grooves 12a of the terminal pins 12 to coincide with both respective side walls of the trapezoidal notches of the insulator 7; each pair of protrusions 12b being formed as a guide for assembly and settlement of the armature unit 8.
In such an electromagnetic relay 1, switching of the contact points is executed by a pivotal movement in a seesaw manner by varying the magnetic flux by energizing the exciter coil 15.
The operation of the non-magnetizing plate 3 will now be described with reference to FIGS. 2A to 2C.
As described above, the electromagnetic relay 1 is switched by energizing the exciter coil 15, and the presence of a non-excited state and an excited state are illustrated schematically in FIGS. 2B and 2C. FIG. 2B designates a non-excited state or ordinary state and FIG. 2C designates an excited state. The movable contact springs 2 are omitted in FIGS. 2B and 2C.
The seesaw balance type electromagnetic relay 1 has terminal pins on both sides, and the relay in FIG. 2B is open and in FIG. 2C is working.
FIG. 2A is an operational characteristic of the relay where a vertical coordinate represents a force and a horizontal coordinate represents a stroke. Numeral 17 denotes a loaded force characteristic of the armature unit 8; 18 is an attractive force characteristic of the electromagnet for the armature unit 8; the upper portion thereof represents the opening side characteristic, and the lower portion represents the working side characteristic. Here, no problem arises when the exciter coil 15 is excited and switched positively from the state of FIG. 2B. However, the attractive force characteristic 18 provides a disadvantage when switching and releasing the excitation of the exciter coil 15 from a working state shown in FIG. 2C to an opening state by the loaded force of the armature unit.
Assuming that the armature 6 is formed entirely of ordinary metal, the armature 6 is magnetized at the time of working to exhibit the characteristic as shown by dotted line 18a and has an attractive force larger than the loaded force, and it becomes impossible to return to the opening state even when the excitation of the exciter coil 15 is released. On the other hand, if a non-magnetizing plate formed of material that cannot be magnetized by the armature 6 is provided, its attractive force exhibits the characteristic as shown by solid line 18b, which is shifted by as much as the thickness of the non-magnetizing plate 3, i.e., by stroke A, to thereby be smaller than that of the loaded force 17, and on releasing the excitation of the exciter coil 15 the armature 6 can be returned to the opening state.
For this reason, the non-magnetizing plate 3 is indispensable for the monostable electromagnetic relay, although the non-magnetizing plate 3 is not necessary for the bistable electromagnetic relay.
FIGS. 3A to 3D illustrate the operation of the bistable electromagnetic relay. In the case of the bistable electromagnetic relay, the armature 6 is only switched by energizing the exciter coil 15, and the armature 6 is not returned to the original state before energizing the exciter coil 15 as shown in FIGS. 3A to 3C. FIG. 3A designates a non-excited state and FIG. 3B designates an excited state in which the armature 6 is switched. FIG. 3C designates a non-excited state in which the armature 6 remains in the same position as in FIG. 3B. FIG. 3D designates an excited state in which the armature 6 is switched. The movable contact springs 2 are also omitted in FIGS. 3A to 3D.
A conventional method of producing an electromagnetic relay 1 will be described with reference to FIGS. 4 and 5 as follows.
In FIG. 4, a plurality of movable contact springs 2 are formed by press-blanking a hoop member 21 formed by connecting bars 25. In the hoop member 21, a pair of reinforcement pieces 24 are formed at the outside of a pair of movable contact springs 2 for stiffening the hoop member 21. Further, positioning holes 23 are provided with the same interval on the connecting bars 25.
An armature 6 having a center protrusion 6a is formed independently of the hoop member 21 also by the press blanking procedure. The center protrusion 6a can be formed at the time of the press blanking.
The hoop member 21 of the movable contact springs 2 and armature 6, respectively, separately prepared are covered with an insulator 27 by an insert mold technique to thereby form a unitary shape. More specifically, the hoop member 21 is set in a recess 26 of a die 20 and the position of the hoop member 21 in the recess 26 is defined by holes 23 on the connecting bar 25 and pins provided on the bottom of the recess 26. Usually, the die 20 has several pairs of positioning pins. Then the corresponding number of armatures 6 is set in each of the deep recesses 27. Setting of the hoop member 21 and the armature 6 in the die is executed by an industrial robot.
In this way, the hoop member 21 and the armature 6 are supported in the die 20, and then a melted insulator is allowed to flow into the die 20 to cool and solidify the insulator, thus the hoop member 21 and the armature 6 are formed in an integrated shape as shown in FIG. 5.
Thereafter, a non-magnetizing plate 3 for upgrading an opening characteristic is fixed on one-side end of the armature 6 by welding or the like, and finally the connecting bars 25 of the hoop member 21 are cut off as shown by dotted lines by dicing or the like to complete the armature unit.
In the above-described conventional method of producing the seesaw balance type microminiature electromagnetic relay, on the insert mold operation, the movable contact springs 2 and the armature 6 must be separately supplied to the die 20 by the industrial robot and supported therein, almost at the same time. Accordingly, the structure of the industrial robot becomes complex when simultaneously required to supply movable contact springs 2 and the armature 6. After the movable contact springs 2 and the armature 6 are integrated together by the insert mold procedure, the non-magnetizing plate previously prepared is welded on the one-side end of the armature 6, accordingly, a troublesome processing for mounting such a small non-magnetic plate is required, and automatic operation also requires a complex and expensive industrial robot.